This application claims the priority of German patent document 102 42 233.8, filed Sep. 12, 2002 (PCT International Application No. PCT/EP2003/009415), the disclosure of which is expressly incorporated by reference herein.
This invention relates to a method for determining a change in volumetric efficiency for an internal combustion engine.
German Patent Document DE 199 34 508 A1 describes a method for controlling exhaust gas recirculation in which a setpoint exhaust gas recirculation quantity is determined based on engine load, engine torque and atmospheric pressure. An actual exhaust gas recirculation quantity and the opening and closing movements of a throttle valve are detected by sensors; and an exhaust gas recirculation control valve is operated as a function of the difference between the actual and setpoint exhaust gas recirculation quantity and a throttle valve opening signal as well as a throttle valve closing signal and the respective air pressure. The determination of the exhaust gas recirculation quantity by sensors is performed by differential pressure measurement by means of a differential pressure sensor at a throttle opening provided in a respective exhaust gas recirculation line.
For exhaust gas recirculation regulation and/or control, it is necessary to know the actual exhaust gas recirculation quantity at every point in time, if possible, and/or the engine operating state. This is particularly important with varying temperature and varying ambient air pressure from the environment from which the fresh gas (i.e., fresh air for the internal combustion engine) is usually obtained. If the actual exhaust gas recirculation quantity is known, the exhaust gas recirculation rate and/or the setpoint exhaust gas recirculation quantity may be regulated at a suitable setpoint exhaust gas recirculation quantity i.e., rate.
The fresh gas quantity fed into the combustion chamber(s) of the internal combustion engine can be measured by a hot-film air-mass flow meter or sensor (HFM) in a fresh gas intake manifold and/or intake path. The total quantity of gas mixture fed into the combustion chamber(s) of the internal combustion engine during engine operation can be determined based on a reference gas mixture quantity determined in advance on a test stand, for example and/or based on a corresponding characteristic line and/or a corresponding engine characteristic map, taking account the prevailing pressure and the prevailing temperature in the intake path. Alternatively, the quantity of gas mixture may also be calculated from the volumetric efficiency by using the ideal gas equation. The actual gas recirculation quantity can be determined by forming the difference between the total quantity of gas mixture fed into the internal combustion engine and the quantity of fresh gas. This actual exhaust gas recirculation quantity can be regulated at a setpoint exhaust gas recirculation quantity by means of an exhaust gas recirculation regulating and/or control system.
Volumetric efficiency is a measure of the fresh gaseous charge; that is, the gas quantity supplied to the internal combustion engine. It is defined as the ratio of the charge feed (i.e., the quantity of gas supplied) to the theoretical charge and/or the quantity of gas theoretically feedable per operating cycle. Volumetric efficiency is thus the ratio of the total fresh charge supplied per operating cycle to the fresh charge in filling the geometric cubic capacity of the internal combustion engine with air and/or a mixture in the ambient state, with the engine not supercharged and/or in the state downstream from a compressor and/or turbocharger or a charging air cooler in internal combustion engines with supercharging. For operation with exhaust gas recirculation, the volumetric efficiency is defined as the ratio of the total quantity of gas mixture supplied per operating cycle to the quantity of gas mixture in filling the geometric cubic capacity of the internal combustion engine with gas mixture in the state after admixture through the exhaust gas recirculation.
The term “quantity” is used in the present case for the sake of simplicity to include a physical parameter indicative of quantity such as that used for the mass or the quantity- or flow rate of recirculated exhaust gas, gas mixture or fresh gas supplied to the internal combustion engine. Volumetric efficiency is also defined as the absorption capacity of an engine.
Since the volumetric efficiency of the internal combustion engine is determined for measured values and/or by appropriate sensors, a change in volumetric efficiency can be attributed to a physical change and/or a false sensor signal. For example, if the reference level of a measurement (i.e., the zero point) and/or a characteristic line of a sensor and/or a measurement instrument changes over a longer period of time, without any apparent external influences, this is referred to as drift and/or a drifting sensor signal. A drifting sensor signal may be incorrectly interpreted as a change in volumetric efficiency due to physical causes.
One object of the present invention is to provide a method of the most accurate possible determination of a change in volumetric efficiency.
Another object of the invention is to provide an application of the inventive method for determining the exhaust gas recirculation quantity for an internal combustion engine having exhaust gas recirculation.
These and other objects and advantages are achieved by the method according to the invention, in which a reference volumetric efficiency is determined in advance. In addition, a first prevailing volumetric efficiency is determined from a first measured value and a second prevailing volumetric efficiency is determined from a second measured value. According to the invention, the first measured value is determined at a rotational speed at which a change in the flow losses in the intake path has only a minor effect on the volumetric efficiency. Consequently the recognized deviation from the reference volumetric efficiency in the first measured value corresponds mainly to a sensor error and/or an incorrectly detected signal. The second measured value is determined at a rotational speed which is above the rotational speed for the first measured value and at which a change in the flow losses also has an effect on the volumetric efficiency. The recognized deviation from the reference volumetric efficiency of the second measured value thus includes a physical change as well as a change caused by a sensor error.
A first and a second prevailing volumetric efficiency are determined from the measured values. According to the invention, the second prevailing volumetric efficiency is corrected by means of the first prevailing volumetric efficiency because this may include a sensor error, which is given as its deviation from the reference volumetric efficiency. It is now possible to determine the physical change in volumetric efficiency for this second prevailing volumetric efficiency, now corrected, and the reference volumetric efficiency.
The inventive method according to the invention may be implemented to advantage in a conventional control unit for in an internal combustion engine, e.g., in a motor vehicle. A higher precision of the calculated volumetric efficiency and/or the calculated change in volumetric efficiency can be achieved through the processing of the sensor signals, thereby permitting a more accurate and thus improved regulation/control of the exhaust gas recirculation quantity and the exhaust gas recirculation rate. Since sensor errors can be detected and taken into account, it is possible to use less expensive sensors and/or meters.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.